Satsuki Kiryuuin is an 18-year-old woman and the Student Council President of Honnouji Academy. She rules the school with an iron fist and assesses the students' abilities, holding the position/authority to assign the powerful Ultima Uniforms. She does not wear a Goku Uniform, stating that her sword, "Bakuzan" is more than enough power and protection.
She wears her "wedding dress," Kamui Junketsu, shortly after finding out Ryuuko possesses her own Kamui.
Major plot spoiler
Honnouji Academy is actually a fortress Satsuki created in order to rebel against her mother, Ragyou, and overthrow the Life Fibers.